clang/win: Fix -Wsign-compare warning after https://codereview.chromium.org/1631903002

chrome/installer/upgrade_test.gyp

 # Copyright (c) 2011 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'variables': {
+    'chromium_code': 1,
     'branding_dir': '../app/theme/<(branding_path_component)',
     'version_py': '<(DEPTH)/build/util/version.py',
     'version_path': '../../chrome/VERSION',
     'lastchange_path': '<(DEPTH)/build/util/LASTCHANGE',
     # 'branding_dir' is set in the 'conditions' section at the bottom.
     'msvs_use_common_release': 0,
     'msvs_use_common_linker_extras': 0,
   },
   'includes': [
     '../../build/win_precompile.gypi',
@@ skipping 69 matching lines @@
           'sources': [
             'test/alternate_version_generator_main.cc',
           ],
           # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
           'msvs_disabled_warnings': [ 4267, ],
         },
       ],
     }],
   ],
 }